1. Field of the Invention
The present invention relates to high frequency electronics. More specifically, the present invention relates to the use of nanoscale devices in active microwave filters and their application to switched channelizers for high frequency multi-function receivers.
2. Description of the Related Art
Although radar and communications receivers are susceptible to both accidental and intentional interference, the effects of this interference may be minimized through the use of radio frequency (RF) filters in the initial stages of the receiver chain. These filters reduce the power of the interfering signals to acceptable levels, which improves sensitivity and enables operation with acceptable signal to noise ratios.
Present systems use miniature thin-film bulk acoustic wave resonator passive filters, which are commonly referred to as “TFR filters” or “FBAR filters.” TFR filters are small, high-Q, and may be used in radar or communications modules. However, they have limited bandwidth (less than 8%) and use discrete components that make integration excessively difficult and expensive. Monolithic inclusion of these passive filters into a Si or GaAs MMIC process would require the addition of piezoelectric thin film materials into the fabrication as well as additional steps. Although current passive filter technologies have suitable dynamic range for microwave applications, they suffer from substantial bandwidth and loss limitations due to the fact that they are not easily MMIC compatible. They must be fabricated on a separate chip and then separately integrated into a transmit/receive module. Therefore, the use of passive filters in a radar or communications receiver can significantly increase not only a receiver's size, but also its cost.
Active filters, wherein the gain from active devices within the filter compensates for losses in passive components, are ideal for use in radar and communications systems. Although they have been studied for many years, active filters have not been used in high performance receivers because their dynamic range is always less than that of the active components. This can be attributed to the non-linear behavior of present active devices. Thus, current active RF filters using either III-V or SiGe transistor technologies have inadequate dynamic range for next-generation radar and communications applications.
Due to their limitations, suitable RF filters are not widely used in current radar and communications systems. However, next-generation multi-function RF systems will include a wideband RF stage, followed closely by a mixer and analog-to-digital converter (ADC) and it is essential that any interfering signals are excluded from the mixer and ADC if operation in a dense interference environment is contemplated. Thus, there remains a need for high dynamic range filters that may be integrated into a MMIC design without substantial added cost or volume.